The subject of the present invention is a process for demounting from its operating rim an assembly formed, firstly, of a tire with radial carcass reinforcement and, secondly, of a removable tread supporting ring, and more particularly an assembly intended to be mounted on an integral rim, at least one of the seats of which is inclined towards the outside.
French Patents FR 2,699,121, FR 2,713,557 and FR 2,713,558 describe a wheel rim which includes, when viewed in meridian section, a first seat, the axially outer end of which is on a circle of diameter less than the diameter of the circle on which the axially inner end is located (such a seat is referred to as being inclined towards the outside), a bearing surface of greater or lesser size intended to receive a removable tread supporting ring, possibly a mounting groove, and a second rim seat which is either identical to or different from the first rim seat. Such rim forms, with a tire, the meridian profile of the carcass reinforcement of which and the shape of the beads of which are adapted, and with a removable tread-bearing support, a high-performance rolling assembly for the case of travel at low pressure or even at zero pressure.
Patent FR 2,720,977 describes a process for mounting a tire, having first and second beads, and the removable tread-bearing support which accompanies it, on an integral mounting rim, having first and second rim seats, at least the first rim seat of which is inclined towards the outside, extended axially onto the outside by a projection of low height, and joined axially onto the inside to a bearing surface intended to receive the tread-bearing support. The disclosed mounting process includes the steps of
firstly introducing the tread-bearing support into the tire, then
presenting on the rim the second bead on the opposite side to the second rim seat, then causing it to pass over the rim bearing surface by means of positioning means, and finally
performing the final mounting stages, such final stages differing according to the specific features of the mounting rim.
If the nominal diameter of the second rim seat is greater than that of the first seat, and in the case of a tread-bearing support of a width less than the axial distance between the inner walls of the two beads, mounting is simple and the possible use of mounting levers to bring the second bead out of its seat, owing to the low forces imposed, does not have any consequence on the integrity of the tire. In contrast, the demounting of such a tire/support assembly involves a sequence of operations, one of which requires the use of demounting levers, i.e., during the phase in which the first or outer bead has to be made to pass out of its seat over the projection or hump formed by the outer edge of the rim. This manual operation requires at least two demounting levers and involves two major disadvantages: (1) the deterioration of the mounting rim due to intense pressure of the levers on the projection, which deterioration is all the greater when the wheel is made of lightweight alloy, and (2) the deterioration of the tire bead in question, by bursting and/or cutting of the rubber forming the outer protective layer located radially beneath the anchoring bead wire of the carcass reinforcement. Such bursting results from the pinching of the rubber between the bead wire and rim seat, which may allow air and/or humidity to pass into the sidewall of the tire via the reinforcement elements of the carcass reinforcement, and thus cause the reinforcement elements to become detached from the liner until the tire is taken out of service.
Overcoming such disadvantages requires at least the use of a single demounting lever, and preferably the complete elimination of the use of such levers, utilizing the opportune fact that the rolling assembly comprises effectively one tread-bearing support.
In order to demount a tire, comprising a first bead and a second bead, and the tread-bearing support which is internal thereto, from an integral mounting rim, comprising a first and a second rim seat, at least the first rim seat of which is inclined towards the outside, extended axially to the outside by a projection of low height and joined axially to the inside to a bearing surface intended to receive the tread-bearing support, the demounting process, according to the invention, comprises the steps of:
pivoting the first bead on its seat around its heel, by the rolling of at least one rotary roller bearing on the bead, so as to create a gap between the toe of the bead and the rim seat,
lubricating the gap thus created,
introducing into the gap a demounting insert in the form of a portion of a circular ring of triangular meridian section, the height of which is at least equal to the radial height of the projection of the rim edge in question, and
using the insert to eject the first bead and the assembly formed of the tire and the tread-bearing support from the mounting rim.
The final stage of the foregoing demounting process can be carried out in various ways, using different means. If the mounting and demounting machine used comprises one or more rotary so-called pressure rollers on either side of the tire/wheel assembly, a thrust is exerted on the second bead in the direction of the axis of rotation of the assembly by means of a rotary roller, such thrust dislodging the second bead from its rim seat and being transmitted to the first bead via the bearing support, thereby permitting dislodgment of the first bead from its seat. The demounting process is terminated by continuing the thrust until the whole of the tire and the support is completely removed.
The foregoing process is perfectly suitable for a mounting machine provided with at least two pressure rollers, one on either side of the tire/wheel assembly. Some machines, however, have only one pressure roller, located on one side only of the assembly. Whether it is a machine with horizontal rotary plates or a machine having a horizontal axis of revolution, it is then necessary to provide an additional stage in the demounting process, which stage consists simply, after placing the demounting insert between the first bead and the rim, of returning the tire/wheel assembly to the machine, such that the rotary roller can exert a pressure force on the second bead.
It is possible that some mounting and demounting machines may have one or more rollers that cannot exert sufficient thrust to dislodge the first bead from its seat. It is then advantageous to use a mounting lever to dislodge the bead, and such a use is accompanied by the use of a demounting insert provided with a lever insertion notch and a rim protection tongue.
The demounting insert may be of plastics material such as polyethylene, polyurethane or another known plastics material. It may also be of elastomeric material of sufficient Shore A hardness, i.e., of between 60 and 95 points.
The preferred length of the plastic insert is between 0.25 and 0.40 times the circumferential length of the bead seat measured at its axially outer end. If such length is less than 0.25 times the circumferential length of the seat, the insert is ineffective. The same applies if the length is greater than 0.40 times the circumferential length of the seat, because this excessive length involves excessive clamping of the tire on the rim provided with the insert.